Photoflash lamp



R. LE R. KREIDLEYR PHOTOFLASH LAMP I Filed Aug. 27

fd-600 'c' FOR /a M//v z/sc Foz 272 mar.

ATTRNEYv Patented Sept. 2, 194i PEQ'LQFLASH LAM? Raymond Le RoyKreidler, Blocmield, N. J., assigner to Westinghouse Electric &Manufacturing Company, East Pittsburgh, Pa., a corporation ofPennsylvania Application August 27, i938, Serial No. 227,074

(Cl. {S7-3l) 4 Claims.

The present invention relates to photoflash lamps which are normallyemployed with cameras for the taking of photographs.

Lamps of this type are known to the art wherein a metal such asaluminum, magnesium or alloys thereof in the form of foil or wire aredisposed in an oxidizing atmosphere within an envelope and ignited bythe passage of an electric current through the lamp. Upon energizationof the lamp, the foil or Wire begins to burn until, after a fractionalpart of a second, complete combustion'occurs with a rise in lightintensity from zero to peak and then a decrease again to zero.

The rate of burning or combustion of the foil or wire is naturallydependent upon its physical characteristics such as weight, thickness,strains, etc. which in turn governs the light output of the lamp andparticularly the duration of the period of peak intensity. Moreover, dueto the mechanical diiculties in producing wire ne enough and foil thinenough to readily burn and ignite easily, the characteristics ofphotoiiash lamps of the prior art have been rather denitely fixed andcould not be modilied at will.

For example, in lamps utilizing aluminum foil, the individual sheets arebeaten as thin as possible, but even after such processing the sheetsare somewhat thicker at the center than at the edges and possessmechanical strains which affect the thermal conductivity oi the foil.Also the light given oli by photoflash lamps employing foil are ofcomparatively short duration with aY high peak intensity, making itsomewhat difiicult to synchronize complete opening of a camera shuttersimultaneously with the moment of peak intensity from the lamp.

In the case of magnesium or aluminum wire mechanical diiculties arelikewise present in that it is difcult to draw wire ne enough, as beforementioned, to readily burn and ignite easily. In addition, lampsemploying magnesium wire have a longer period of peak intensity than doaluminum foil lamps, lthus facilitating synchronization with a camerashutter; but in contradistinction to aluminum foil lamps, the intensityof magnesium wire lamps is much lower.

vIt is accordingly an object of the present invention to provide aphotoflash lamp wherein the rate of burning of the light producingmaterial and thus the intensity and duration of the ash can becontrolled.

Another object of the present invention is the provision of a photoflashlamp employing a combustible material in the form of wire or foil fromwhich cold working strains have been removed by annealing the material.

Another object of the present invention is the provision of a photoflashlamp wherein the combustible material is blended so as to possess apreselected combustion rate giving a desired period of peak intensity ofillumination to facilitate synchronization of the photoliash lamp with acamera shutter.

A further object of the present invention is the Yprovision of aphotoflash lamp wherein the combustible material is annealed and beatenin such .characteristics is employed in order to control the combustionrate and the period of peak intensity of illumination.

Fig. 2 is an elevational view of a modilication which the presentinvention may take and diflfers from that of Fig. 1 merely in theutilization of combustible material in the form of wire i lieu of foilas in Fig. 1. Fig. 3 is a cross-sectional view of the combustiblematerial, either in the form of wire or foil,

treated in accordance with the present invention.

Fig. 4 is a graphic illustration depicting what has been termed onegrade of combustible material in the form of foil or leaf showing therelationship of rate of combustion in milliseconds to internationalphotographic units intensity at diierent periods of treatment.

Fig. 5 is a graphic illustration depicting another grade of combustiblematerial showing 'the same relationship as that of the grade of Fig. 4,and

Fig. 6 is a graphic illustration depicting the relationship of rate ofcombustion in milliseconde to international photographic units intensityat different periods of treatment and wherein the combustible materialas employed in the photoflash lamp is blended so as to give a controlledrate of combustion with attendant peak intensity.

Referring now to the drawing in detail, the photoflash lamp as shown inFig 1 comprises an envelope 5 provided with the usual screw base t toenable it to be disposed in a socket for supplying electrical energythereto. An ignition element 'l is disposed interiorly of the envelopewhich, when energized, initiates combustion of the combustible material8 in the form of metallic foil, such as aluminum leaf, in the presenceof an oxygenic atmosphere within the envelope. The envelope is, providedwith a reentrant stem through which the leading-in conductors for theigniter element are sealed and a baille member Ill rests upon the stemto prevent the hot products of combustion from falling in the vicinityof the seal which otherwise might cause explosion of the envelope. Thelamp shown in Fig. 2 is substantially identical to that shown in Fig. 1with the exception that the combustible material B in this modificationis in the form of metallic wire, such as magnesium or the like.

Aluminum foil, as hereinbefore mentioned, is the most universally usedcombustible material in leaf form for photoash lamps, while magnesium iscustomarily used in wire form. However, in the working of the foil intoleaf form the foil is beaten as thin as it can be worked, but suchprocess has always resulted in the individual leaves being thicker atthe center than at the edges. The following table shows the variation inthickness of different grades of foil of the same dimensions, and sinceit is diiiicult to measure by any linear scale, thickness is given inmilligrams per square inch for comparative purposes:

TABLE I Thickness Thickness Total weight LCM grade in center at edge ofleaf JmL/sq. in. MgJsq. in. Millgrams l. 010 732 20 1. 137 895 25 1.350975 28 1.63 1.300 4l 1.16 1. 30 4l 2. 56 1.38 48 1.48 1. 46 48 It iswell recognized that the rate of combustion of aluminum foil isVdependent upon its thickness. Since such foil has heretofore beenthicker in the center than at the edges, the greater portion of itscross-sectional area, when the leaves are folded into the envelope, isin close proximity to the igniter element which burns very slowly. Thisis due to the fact that the foil is so thin that it cannot be touched byhuman hands without deteriorating into a powder. Consequently, thesheets are picked up by friction on a stick and pushed or stuffedthrough a funnel and the neck of the envelope into the bulbous portionthereof which thus inherently folds over the edges of the sheet as thecenter is pushed into the envelope adjacent the igniter element.Experiments have shown that the rate of combustion and consequently thelight output characteristics of a photoflash lamp may be controlled bybeating the foil so that the center of the leaf is very thin, while theedge of the leaf can be much thicker, such as shown in Fig. 3.

This accordingly places the thin center portion of the leaf, whenfolded, in such position as to be in close proximity to the igniterelement so that it is easily ignited and burns rapidly, while the thickportion burns more slowly which increases the duration of light output.Thus by controlling the thickness of the leaf the light output of thephotoash lamp may likewise be controlled.

For comparison purposes foil so beaten is shown inthe foregoing tablewherein it will be noted that grade 4A has been beaten in the center soas to be thinner than grade 4, although the edges are of the samethickness and the total weight of the leaf remains the same as grader/l.The same may be said of grade 5A which shows the center of the leaf tobe considerably thinner than grade 5, while the edges have also beenslightly increased in thickness over that of grade 5, although the totalweight of grade 5 and 5A is the same.

In addition to controlling the light output characteristics by formingthe sheets in the manner above described, tests have shown that heattreating of the foil or wire also controls such characteristics. Forexample, the following table indicates the effect of heat treatment onpeak light output characteristics of the various grades (thickness) offoil:

TABLE II Peak I. P. U. (international photographic units) Heat treatedIt will .be noted from the foregoing table that in each instance thepeak intensity of each grade leaf is increased from to 1000% or more bythe expedient of heat treating which, as before stated, removes the coldworking strains resulting in an increase in peak intensity. Moreover,the increase in peak intensity is controllable by the ratio oftemperature and time combinations as shown by the following table of twogrades of leaf of slightly varying thicknesses:

TABLE III Peak I. P. U.

Leaf heated for f Not 10 mm. nt

Leaf grade heated 23212916? t 55m-600 o.

76, 200 142, too 71, 40o 152, 200 76,200 147, 500 76, 200 152, 50c

In each of the above grades, although originally and unheated, ofappreciable difference in peak intensity, it will be observed thatregardless of the temperature and period of heat treatment, the peakintensity is not only increased but the intensity is made substantiallyuniformV for each period-temperature. Also, the peak intensity increaseswith increased temperature and inversely to the time period oftreatment.

By reference to Fig. 4, wherein the abscissa represents time inmilliseconds from closing of the electrical circuit until completion ofthe flash, and the ordinate represents international photographic unitsin thousands, the relationship of increase in peak intensity ascontrolled by heat of the flash lasting for approximately milliseconds.

However, by heat treating this grade 3 leaf for 2%; hours at atemperature of 215 C., the peak intensity is increased, as shown by thecurve B, to approximately '79,000 i. p. u. and since the ilash begins atapproximately 18 milliseconds and lasts until approximately 58milliseconds, there is a substantial increase in lumensseconds or lightoutput as represented by the total area of the curve B. Again byincreasing the temperature with an inverse variation in the time of heattreating, as shown by the curve C of Fig. 4, a still further increase inpeak intensity results approximating 150,000 i. p. u. and the flashbegins at approximately 15 milliseconds following energization of thelamp and lasts until approximately milliseconds or a total time periodof 30 milliseconds. Thus there is a still further increase in totallight output or lumenssecond as represented by the total area of curveC. It is also to be noted that the minimum and maximum peak intensity ofa grade 3 leaf is shown in dotted lines in connection with curve C todepict the degree of variation due to slight dierences in thickness, butsuch have not been shown in connection with curves A and B for purposesof simplicity.

Fig. 5 is similar in every respect to Fig. 4 with the exception that thecurves represent a grade 5 leaf which, as will be noted from Table I, isthicker than that of grade 3, which accounts for a slightly lower peakintensity and a longer period of time before ignition and completecombustion.

In addition to controlling the light output characteristics of photoashlamps by heat treatment of the aluminum foil, I have found that byblending the leaves the characteristics may be substantially controlledat will. The following l.

table will serve to illustrate the effect of blending both on peakintensity as well as time lag to various points on the curve andduration of specic peak intensities:

TABLE IV Peak i. p. u.

Heat treated Not heat Leaf gwdg treated 550 I16 Q MillisecondsMilliseconds duralag toation at- Leaf grade Peak i. p. u.

M i. p* u. Peak 50M 1. p. u. 100M 1 (not heated) 17.0 20.6 85.000 7.18 2(not hcated) 20.6 23. 5 162,000 9. 5 5. 23 1+2(notheated) 24.6 27.4 71,500 8.36 l+3 (notheated). 18.8 21.1 62,000 5. 50 1-l-4 (notheated) 19.222.6 56,500 2. 2S 1 (not heated) +3 (heated). 18. 2 22.4 131,000 9,64 2.5 l (not heated) +4 (heatedLi. 22.2 25.1 87, 300 6. 6 1.07 2|3 (bothheat- Also in Fig. 6 the result of a blending of various grades ofaluminum leaf is graphically shown. In the particular instanceillustrated in Fig. 6 the various curves have been compiled from grade 3and grade 5 as shown in Figs. 4

and 5. Hence, curve A represents the results obtained by utilizingunheated grade 3 and 5,

It will thus be seen from the foregoing that' the rate of combustion ofaluminum foil and consequently the light output characteristics of aphotoflash lamp may be controlled first by beating the individual sheetsso that they are thinner at the center than at the edges. Since thethinner portion is disposed in close proximity to the igniter elementwhen the leaves are folded in the envelope, they are easily ignited andburn very rapidly, while the thicker edges burn more slowly, whichincreases the duration of light output.

Secondly, the light output characteristics may be further controlled byheat treating the leaves over a comparatively Wide temperature range ininverse proportion to the time period of treatment. Moreover, byblending the various grades of leaf, each of which have been givenpreselected light output characteristics, a photoflash lamp can be madein accordance with the present invention wherein the light outputcharacteristics can be controlled substantially at will so that the lampmay be readily synchronized with any camera shutter. It is to beunderstood that although the utilization of aluminum foil as thecombustible material has been described in detail as the preferredembodiment of the present invention, it nevertheless applies with equalfacility to aluminum or magnesium in wire form which can likewise be sodrawn as to have portions of smaller diameter than other portions,heated, treated and blended.

Although two modifications of the present invention have been shown anddescribed, other embodiments thereof may be made Without departing fromthe spirit and scope of the appended claims.

I claim:

l. A photolash lamp comprising a sealed envelope provided With a gascontaining oxygen, an ignitor element in said envelope, and combustiblematerial disposed in said envelope in close proximity to said ignitorelement and combustible with the oxygen in said envelope when saidignitor element is supplied with electrical energy to produce amomentary intense light, said material having a reduced cross-section inthe center thereof thinner than the edge portions, and said materialbeing disposed in the envelope, an-d folded to position the greaterportion of the thinned area thereof in closer proximity to the ignitorelement than the thicker edge portions of said material.

2. A photolash lamp comprising a sealed envelope provided with a gascontaining oxygen, an ignitor element in said envelope, and combustiblematerial disposed in said envelope in close proximity to said ignitorelement and combustible with the oxygen in said envelope when saidignitor element is supplied with electrical energy to produce amomentary intense light, said material comprising a plurality ofmetallic foil sheets having a thin center portion of less thickness thanthe edges thereof and devoid of cold working strains to increase thepeak intensity and combustion rate of the individual sheets, and saidindividual sheets having diiTerent preselected intensity and combustioncharacteristics and blended to impart to the material a desired peakintensity and rate of combustion.

3. The method of controlling the rate of combustion and increasing thepeak intensity of a photofiash lamp charge Which consists in reducingthe thickness of the center of a plurality of foil sheets some of whichare thicker than others, heat treating such sheets for a preselectedtime period and at a preselected temperature to remove cold Workingstrains and impart a predetermined peak intensity and combustion ratecharacteristic to each individual sheet, and blending the heat treatedfoil sheets of different characteristics in composing the charge toproduce a charge having a desired combustion rate and intensitycharacteristics.

4. The method of controlling the rate 0f combuston and increasing thepeak intensity of a photoash lamp charge .which consists in reducing thethickness of the center of a plurality of foil sheets some of which arethicker than others, heat treating such sheets for a preselected timeperiod and at a preselected temperature to remove cold Working strainsand impart a predetermined peak intensity and combustion rate to eachindividual sheet, blending the heat treated foil sheets of differentcharacteristics in composing the charge to produce a charge having adesired combustion rate and intensity characteristic, and positioningthe thincenter portions of the sheets in closer proximity to the ignitorelement of the lamp than the thicker edge portions thereof.

RAYMOND LE ROY KREIDLER.

